DOUBLE EDIT: So I'm kind of confused as to how to make this work. Not the plugin, that's quite simple, but getting the resolution of the image right. I have a tiny map (20x20) and I used the MV "Save map as image" thing, and then tinkered with it in Photoshop, and then put an ! in front of its filename and threw that in the Parallax folder, but when I select "View in editor" the paralax is 1/4th the size, and looped 4 times on the screen. What am I doing wrong there?

The TDDP_BindPicturesToMap plugin worked perfectly for me. Make sure to have no looping turned on (unless you want it) and it's 1:1. You can use the picture as a parallax background for placing boundaries and events but turn it off later when it isn't necessary. Works better than the inbuilt ! parallax lock I've found.